Distribution and genetic diversity of Beauveria species at different soil depths in natural and agricultural ecosystems

This study aimed to analyze vertical distribution and diversity of Beauveria species throughout the soil profile within farmland and forest habitats to obtain an accurate view of Beauveria density and diversity associated with a particular soil layer. The analysis included a total of 72 soil samples collected at four depths: 0–5, 5–10, 10–15, and 15–20 cm. Of the soil samples, 43 (60%) were positive for Beauveria, producing a total of 641 isolates. Of the positive samples, 28 (65%) were from depths of 0–5 and 5–10 cm while only 15 (35%) from depths of 10–15 and 15–20 cm. Further, for the 29 negative samples, 21 (72%) of them were from depths of 10–15 and 15–20 cm. Higher fungal frequency was found in forest habitat, 462 isolates in 21 positive samples (72%), than from farmland, 179 isolates in 22 positive samples (28%). The highest fungal density (577 isolates, 90%) was recorded in the two top layers (0–5 and 5–10 cm) and decreased significantly as the soil depth increased. Only two species B. bassiana and B. pseudobassiana were identified and co-habited along the whole soil profile. Beauveria pseudobassiana was more strongly affiliated with forest (79%) than farmland (27%) and vice-versa for B. bassiana (21% and 73%, respectively). For both species, the haplotypic diversity varied throughout the soil profile and the highest diversity values were recorded within the soil depths 0–5 and 5–10 cm. This study suggested that the soil band 0–10 cm could be adopted as the standardized depth for soil sampling for ecological studies of Beauveria. It will be important to perform exhaustive soil sampling in different seasons and at different soil depths to validate this hypothesis.